Novel,promising, and broadband microwave-absorbing nanocomposite based on the graphite-like carbon nitride/CuS

In this study, a broadband, intense, novel, and promising microwave-absorbing nanocomposite was prepared using graphite-like carbon nitride (g-C₃N₄)/CuS suspended in poly(methyl methacrylate) (PMMA) medium. The g-C₃N₄ nanosheets were synthesized by heating the urea as well as the CuS nanoparticles, and g-C₃N₄/CuS nanocomposites were prepared using a solvothermal method and then were separately molded by a PMMA solution to investigate their microwave-absorbing characteristics. The Fourier transform infrared and X-ray powder diffraction were used to characterize the g-C₃N₄, CuS, and CuS/g-C₃N₄ nanostructures, which confirmed that the pure structure of the nanomaterials has been synthesized. The optical properties of the nanostructures were also investigated by diffuse reflection spectroscopy analysis. Accordingly, the Kubelka–Munk theory suggested significant narrow band gap for g-C₃N₄/CuS nanocomposite (0.27 eV), facilitating electron jumping and conductive loss. The morphology of the structures was examined using field emission scanning electron microscopy micrographs, illustrating that the uniform hexagonal structures of the CuS nanoplates have been formed and the CuS two-dimensional structures were uniformly distributed on the g-C₃N₄ nanosheets. Finally, the microwave-absorbing properties of the CuS, g-C₃N₄, and g-C₃N₄/CuS were investigated by PMMA as a host. The microwave-absorbing properties were evaluated using a vector network analyzer. The results illustrated that the maximum reflection loss of the g-C₃N₄/PMMA nanocomposite was −71.05 dB at 14.90 GHz with a thickness of 2.00 mm, demonstrating a 1.70 GHz bandwidth >30 dB, as well as g-C₃N₄/CuS/PMMA nanocomposite absorbed 7.30 GHz bandwidth of more than 10 dB with a thickness of 1.80 mm along the x- and ku-band frequency. The obtained results introduced the PMMA as a capable microwave-absorbing substrate. Besides, the g-C₃N₄/CuS/PMMA nanocomposite demonstrated metamaterial property and abundant attenuation constant. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48430.     

Role of the particle size of graphite-like boron nitride in nucleation of cubic boron nitride

The influence of the reduced radius of grains of the graphite-like hexagonal boron nitride (h-BN) on the nucleation of the cubic boron nitride (c-BN) during synthesis from an initiator solution at a high pressure is analyzed. The colloidal mechanism of nucleation is confirmed experimentally. It is shown that there is a correlation between the nucleus sizes of the hexagonal boron nitride and the pressure of the onset of nucleation of the cubic boron nitride. The effect of these sizes of the hexagonal boron nitride on the concentration of crystal nuclei of the cubic boron nitride is studied. The kinetic nucleation curves are obtained. It is demonstrated that the concentration of crystallization centers depends on the thermodynamic and kinetic parameters, as well as on the particle size of the graphite-like hexagonal boron nitride. Original Russian Text ? S.P. Bogdanov, 2008, published in Fizika i Khimiya Stekla.     

Features of the synthesis of carbon nitride oxide (g-C3N4)O at urea pyrolysis

First from urea was synthesized carbon nitride oxide (g-C₃N₄)O which is formed in a vapor gas reactionary space and is deposited outside of a place of precursor localization. The reaction of urea conversion was investigated in an interval of temperatures 350–450 °С, but carbon nitride oxide is detected in the products of pyrolysis only at temperatures above 430 °С. Carbon nitride oxide is dissolved in water and at a reducing it by hydroquinone is formed reduced carbon nitride oxide consisting, as we believe, from azagraphene sheets.     

Rapid synthesis of water-soluble carbon nanotubes-supported PtRu nanoparticles for methanol electrooxidation

A one-pot, rapid microwave-assisted method is proposed to directly synthesize water-soluble surface-aminated carbon nanotubes (CNTs-NH₂) from pristine CNTs by covalently grafting ethylenediamine onto the surface of CNTs, requiring no cumbersome chemical oxidation of CNTs. The excellent water-solubility and abundant surface functional groups of the CNTs-NH₂ lead to the production of uniformly dispersed PtRu nanoparticles (NPs) with diameter ranging from 1.5 to 4.5 nm. Cyclic voltammetry and amperometric studies indicate that the resulting PtRu NPs/CNTs-NH₂ nanohybrids have higher electrochemical surface area, better electrocatalytic performance and higher stability towards methanol oxidation compared to PtRu NPs supported on the pristine CNTs. The high electrocatalytic performance is mainly contributed to the small particle size and high dispersion of PtRu NPs and good proton conductivity of CNTs-NH₂. This work may demonstrate a universal approach to fabricate superior metal nanocrystalline on CNTs for broad applications in energy systems and sensing devices.     

Controlled synthesis of graphitic carbon nitride/beta bismuth oxide composite and its high visible-light photocatalytic activity

g-C₃N₄/β-Bi₂O₃ composites with high visible-light-driven photocatalytic activity were prepared through calcination of g-C₃N₄/Bi₂O₂CO₃ of different proportions. They were characterized by powder X-ray diffraction (XRD), Fourier Translation infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy TEM (high resolution transmission electron microscopy HRTEM), UV–vis diffuse reflectance spectra (UV–vis DRS) and photoluminescence spectra (PL) techniques. It was observed that the phase structure of Bi₂O₃ is subject to the amount of g-C₃N₄ in the g-C₃N₄/Bi₂O₂CO₃ precursor. Based on the results of light absorption and photocurrent measurement as well as the energy levels of β-Bi₂O₃ and g-C₃N₄, we propose a mechanism for the degradation of organic compounds over this class of catalysts.     

Estimation of thermodynamic stability conditions and perspectives for synthesis of covalent carbon nitride

The present work is devoted to the determination of conditions of thermodynamic stability of carbon nitride having structure of β-C₃N₄. The thermodynamic functions of crystalline covalent carbon nitride required for thermodynamic reckoning of parameters of formation of carbon nitride were determined on the base of the Debye theory with the characteristic temperature varied in the range from 1000 K to 2500 K. The formation enthalpy of carbon nitride was estimated on the base of the energy of atomization and formation enthalpy of a mixture of atomized carbon and nitrogen. The resulted quantity of the standard formation enthalpy of covalent carbon nitride at 298.15 K made up 4.47 kcal/mol. Thermodynamic computations were accomplished with the use of the Automated System of Thermodynamic Reckonings and Algorithms ASTRAL. Behavior of the gaseous phase of a chemical system was described by the BKW-RR equation of state. Carbon nitride was considered to be incompressible. The region of thermodynamic stability of covalent carbon nitride is computed. It is shown that in contrast to the carbon condensation into graphite the pressure of condensation of β-C₃N₄ when adding other chemical elements to a thermodynamic system can not only increase but decrease as well. Consideration of detonation and explosion processes in high explosives shows a way for practical synthesis of covalent carbon nitride.     

Carbothermal synthesis of boron nitride coating on PAN carbon fiber

Boron nitride (BN) thin coating has been formed on the surface of chemically activated polyacrylonitrile (PAN) carbon fiber by dip coating method. Dip coating was carried out in saturated boric acid solution followed by nitridation at a temperature of 1200 °C in nitrogen at atmospheric pressure to produce BN coating. Chemical activation improved surface area of PAN fiber which favours in situ carbothermal reduction of boric acid. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) have shown the formation of boron nitride. The X-ray photoelectron spectroscopy reveals that the coating forms a composite layer of carbon, BN/BO_xN_y and some graphite like BCN with local structure of B–N–C and B(N–C)₃. The oxidation resistance of the coated fiber was significantly higher than uncoated carbon fiber. Tensile strength measurement reveals that the BN coated fiber maintained 90% of its original strength. As compared to chemical vapor deposition (CVD), this process is simple, non-hazardous and is expected to be cost effective.     

One-step ultrasonic synthesis of water-soluble carbon nanoparticles with excellent photoluminescent properties

Monodispersed water-soluble fluorescent carbon nanoparticles (CNPs) were synthesized directly from glucose by a one-step alkali or acid assisted ultrasonic treatment. The CNPs were characterized by transmission electron microscopy, optical fluorescent microscopy, fluorescent spectrophotometry, fourier transform infrared spectrophotometry and ultraviolet-visible spectrophotometry. The results showed that the particle surfaces were rich in hydroxyl groups, giving them high hydrophilicity. The CNPs could emit bright and colorful photoluminescence covering the entire visible-to-near infrared (NIR) spectral range. Notably, the NIR emission of the CNPs could be obtained by NIR excitation. Furthermore, these CNPs also had excellent up-conversion fluorescent properties.     

Facile synthesis of Y-doped graphitic carbon nitride with enhanced photocatalytic performance

Yttrium-doped graphitic carbon nitride (Y/g-C₃N₄) catalysts were prepared via a facile pyrolysis method with urea used as a precursor and yttrium nitrate as the Y source. Characterization results show that an appropriate doping ratio of Y can be embedded into in-planes of g-C₃N₄. The Y/g-C₃N₄ catalysts are characterized by hierarchical porosity, large specific surface area, and large pore volume. Introduction of Y species effectively extends the spectral response of g-C₃N₄ from ultraviolet to visible region and decelerates the recombination of photogenerated electrons and holes. Because of these properties, the Y/g-C₃N₄ catalysts show an enhanced photocatalytic performance in rhodamine B degradation under visible light.     

Osteoinduction properties of graphite-like amorphous carbon films evaluated in-vitro

Graphite-like amorphous carbon (a-C) films were deposited by magnetron sputtering on medical grade stainless steel (SS) substrates. The purpose of the study was the evaluation of amorphous carbon as a coating for medical implants in contact with bone, in which the formation of bone on the surface is of special interest to improve the implant performance. The initial step consisted of the evaluation of the cytocompatibility of the a-C films. Cytocompatibility was evaluated by seeding human osteoblast cells on the surfaces and measuring their adhesion, proliferation and viability up to seven days. These data are also of interest for the osteoinduction process because the initial phase of the bone-forming activity of osteoblasts entails the attachment, proliferation, cell differentiation and extracellular matrix synthesis, followed by a second phase of bone matrix mineralization. The evaluation in-vitro of the osteoinduction properties of the surfaces consisted on the study of cell differentiation by measuring the alkaline phosphatase activity, the morphological examination of the mineralized extracellular matrix by electron microscopy, and the evaluation of a selection of proteins involved in the bone-formation process.The cytocompatibility (cell attachment, proliferation and viability) was determined in comparison with SS, titanium coatings and the plastic tissue control. We observed a superior cellular adhesion and proliferation in the a-C surfaces, while the viability was slightly better on the Ti coatings, but nevertheless, the a-C values were much higher than in the plastic control, indicating that the a-C films are no toxic and biocompatible. On the other hand, all the results of the osteoinduction; ALP specific activity and expression of bone-growth specific proteins indicated that the a-C surface significantly promotes the cell differentiation, leading to the formation of the extracellular matrix and its mineralization.     

Application of nanocrystalline graphite-like pyrolytic carbon film electrode for voltammetric sensing of lead

A nanocrystalline pyrolytic carbon film was employed as working electrode to detect micromolar-level concentrations of lead by anodic stripping voltammetery as an example of its potential applications in environmental analysis. The response was compared with conventional carbon-based electrodes such as glassy carbon, edge-plane pyrolytic graphite, and basal-plane pyrolytic graphite electrodes. The favorable properties of this carbon coating for Pb detection lie in its high degree of sensitivity, high response stability, low memory effect, and a good repeatability. The applicability of this sensor was tested on spiked tap water and river water samples.     

Controllable and large-scale synthesis of metal-free carbon nanofibers and carbon nanocoils over water-soluble NaxKy catalysts

Through the pyrolysis of acetylene at 450 °C, large quantities of carbon nanocoils or carbon nanofibers can be synthesized selectively by controlling the Na:K molar ratio of water-soluble Na_xK_y catalysts. We found that the temperature adopted for pyrolysis is an important factor for selectively obtaining the different kinds of products. Because the Na_xK_y catalysts are water-soluble, they can be easily removed, and the nanocarbon materials can be harvested undamaged in high purity. The process is simple, inexpensive, and environment-benign, giving a product yield matching those of the transition-metal catalysts. Based on the results, we conducted discussion on the role of catalyst, effect of pyrolysis temperature, and formation mechanism of the nanomaterials.     

Solvothermal synthesis of two-dimensional graphitic carbon nitride/tungsten oxide nanocomposite: a robust electrochemical scaffold for selective determination of dopamine and uric acid

Journal of Applied Electrochemistry - A glassy carbon electrode was modified with a 2D-networked nanostructure composed of graphitic carbon nitride and tungsten oxide nanoparticles (2D-g-C3N4/WO3)...     

Influence of the thermal process of carbon template removal in the mesoporous boron nitride synthesis

Influence of the thermal process involved in the carbon template elimination during the synthesis of mesoporous boron nitride by using nanocasting process of a mesoporous CMK-3 carbon with a borazinic precursor is presented. The borazinic precursor, the tri(methylamino)borazine (MAB), is converted to boron nitride (BN) inside the mesopores of a CMK-3 mesoporous carbon template by ceramization under nitrogen or under ammonia. The carbon template elimination is carried out by thermal treatment under air or under ammonia. The X-ray diffraction, TEM and pore size analysis are used to study the texture of the boron nitride synthesized from the carbon template. A template elimination performed by hydrogenation with an ammonia treatment allows to obtain an organized porous structure, which is not possible by using an oxidation treatment. In order to preserve the mesoporous organization of boron nitride, a two steps procedure (ceramization followed with template elimination by hydrogenation) is more efficient than a one step procedure (ceramization and template hydrogenation simultaneously).     

Controllable synthesis and purification of carbon nanofibers and nanocoils over water-soluble NaNO3

In order to avoid the complicated purification process of carbon nanomaterials (CNMs) and obtain high-purity CNMs, NaNO₃ powder was used as catalyst for the synthesis of CNM. By controlling the decomposition temperature (400 and 450 °C), liner carbon nanofibers and helical carbon nanofibers can be selectively synthesized. Because of the used catalyst is water-soluble, it can be removed easily from the products by water washing and high-purity CNMs can be obtained undamaged. It is worth pointing out that the use of water-soluble salts as catalyst is new and the approach bypasses the scabrous problems related to CNM purification.     

Two-dimensional graphitic carbon nitride for membrane separation

Recent years, membrane separation technology has attracted significant research attention because of the efficient and environmentally friendly operation. The selection of suitable materials to improve the membrane selectivity, permeability and other properties has become a topic of vital research relevance. Two-dimensional (2D) materials, a novel family of multifunctional materials, are widely used in membrane separation due to their unique structure and properties. In this respect, as a novel 2D material, graphitic carbon nitride (g-C₃N₄) have found specific attention in membrane separation. This study reviews the application of carbon nitride in gas separation membranes, pervaporation membranes, nanofiltration membranes, reverse osmosis membranes, ion exchange membranes and catalytic membranes, along with describing the separation mechanisms.     

Improvement of electrical conductivity of silicon nitride/carbon nano-fibers composite using magnesium silicon nitride and ytterbium oxide as sintering additives

In order to find out the influence of sintering additives on the electrical conductivity of Si₃N₄-based ceramics composites with dispersed carbon nano-fibers (CNFs) two different mixtures of sintering additives were tested – Al₂O₃/Yb₂O₃ and MgSiN₂/Yb₂O₃, respectively. Optimization of hot-pressing conditions was performed for each mixture. The results show that the electrical conductivity can be effectively increased up to 1315 S/m by replacement of traditional sintering aid – alumina, with magnesium silicon nitride, while the mechanical properties remained on the same level. Other advantages of using MgSiN₂ instead of alumina are the preservation of higher amounts of CNFs in the ceramic composite and lower densification temperature (1500 °C) compared to samples sintered with alumina-based sintering aids (1550 °C).     

Water-tolerant graphene oxide as a high-efficiency catalyst for the synthesis of propylene carbonate from propylene oxide and carbon dioxide

Graphene oxide (GO) was found to be a metal-free, water-tolerant and high-efficiency catalyst towards the cycloaddition of carbon dioxide (CO₂) to propylene oxide (PO) for the synthesis of propylene carbonate (PC) at room temperature (RT) and atmospheric pressure without the need for a solvent. Using GO as catalyst and tetrabutylammonium bromide (Bu₄NBr) as co-catalyst, PO is rapidly converted to PC with 96% yield and 100% selectivity under relatively mild conditions (100 °C, 2.25 MPa, 1 h). The effects of catalyst amount, temperature, time and water (H₂O) addition on the reaction were investigated. It is found that the presence of a proper amount of H₂O enhances the conversion of epoxide remarkably. A comparison of the catalytic activities of a number of reduced graphene oxide (r-GO) samples under similar reaction conditions revealed that it is the hydroxyl groups (rather than the carboxyl groups) on GO that form hydrogen bonds with PO, and act synergistically with halide anions to promote the cycloaddition reaction. A possible mechanism is proposed.     

Zinc oxide quantum dots/graphitic carbon nitride nanosheets based visible-light photocatalyst for efficient tetracycline hydrochloride degradation

Journal of Porous Materials - A simple liquid phase self-assembly method was successfully developed to prepare 0D/2D nanocomposites based on ZnO QDs/g-C3N4 nanosheets. The structural...     

Mechanosynthesis of carbon nitride compounds

In the present paper we report the formation of CN_x phases during mechanical treatment of graphite in a nitrogen atmosphere. Samples containing approximately 25 wt.% of CN_x phases have been obtained with the experimental conditions presented in this work. The formation of carbon–nitrogen bonds has been proved by infrared (IR) and X-ray photoelectron spectroscopy (XPS). In addition, thermogravimetric analysis (TGA) shows that the mechanosynthesized CN_x materials decompose to molecular nitrogen at temperatures above 873 K.